1,728,887 research outputs found
Plastic ice in confined geometry: the evidence from neutron diffraction and NMR relaxation
Full text linkNeutron diffraction and nuclear magnetic resonance (NMR) relaxation studies have been made of water/ice in mesoporous SBA-15 silica with ordered structures of cylindrical mesopores with a pore diameter similar to 8.6 nm, over the temperature range 180-300 K. Both measurements show similar depressed freezing and melting points due to the Gibb-Thomson effect. The neutron diffraction measurements for fully filled pores show, in addition to cubic and hexagonal crystalline ice, the presence of a disordered water/ice component extending a further 50-80 K, down to around or below 200 K. NMR relaxation measurements over the same temperature range show a free induction decay that is partly Gaussian and characteristic of brittle ice but that also exhibits a longer exponential relaxation component. An argument has been made (Liu et al 2006 J. Phys:. Condens. Matter 18 10009-28; Webber et al 2007 Magn. Reson. Imag. 25 533-6) to suggest that this is an observation of ice in a plastic or rotationally mobile state, and that there is a fully reversible inter-conversion between brittle and plastic states of ice as the temperature is lowered or raised. More recent detailed NMR measurements are also discussed that allow the extraction of activation enthalpies and an estimate to be made of the equilibrium thickness, as a function of temperature, if the the assumption is made that the plastic component is in the form of a layer at the silica interface. The two different techniques suggest a maximum layer thickness of about 1.0-1.5 nm
Synthesis, crystal structure and properties of the new superconductors TaRuB and NbOsB
No full textTwo new ternary compounds TaRuB and NbOsB were synthesized by arc-melting and annealing at 1500–1850 °C. They crystallize in orthorhombic primitive structures with space group Pbam . Magnetic susceptibility, electrical resistivity, and specific heat measurements reveal bulk superconductivity for metallic TaRuB with a IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn001.gif] {{T}_{̑ext{c}}}≈ 4} K. Electronic structure calculations by DFT methods show that 4 d and 5 d transition-metal states dominate the density of states (DOS) at the Fermi level IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn002.gif] {{{E}_{̑ext{F}}}} with a pronounced quasi one-dimensional behaviour along the [0 0 1] direction. Comparison of the calculated DOS at IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn003.gif] {{{E}_{̑ext{F}}}} with specific heat data reveals a moderate electron–phonon coupling. Possible small boron vacancies could significantly reduce the DOS at IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn004.gif] {{{E}_{̑ext{F}}}} , hence decrease IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn005.gif] {{{T}_{̑ext{c}}}} for samples annealed at higher temperatures. For NbOsB, the DOS( IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn006.gif] {{{E}_{̑ext{F}}}} ) is strongly reduced due to an increase of covalent bonding interactions between Os and B. Accordingly, a lower IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn007.gif] {{{T}_{̑ext{c}}}} IMG [http://ej.iop.org/images/0953-8984/27/41/415701/cmaa0309ieqn008.gif] {≈ 1 K is observed
Absence of low energy magnetic spin-fluctuations in isovalently and aliovalently doped LaCo<sub>2</sub>B<sub>2</sub> superconducting compounds
No full textMagnetization, resistivity and 11 B, 59 Co NMR measurements have been performed on the Pauli paramagnet IMG [http://ej.iop.org/images/0953-8984/28/34/345701/cmaa2a4dieqn001.gif] ̑ext{LaC}{{̑ext{o}}_{2}}{{̑ext{B}}_{2}}} , and the superconductors IMG [http://ej.iop.org/images/0953-8984/28/34/345701/cmaa2a4dieqn002.gif] {̑ext{L}{{̑ext{a}}_{0.9}}{{̑ext{Y}}_{0.1}}̑ext{C}{{̑ext{o}}_{2}}{{̑ext{B}}_{2}}} ( IMG [http://ej.iop.org/images/0953-8984/28/34/345701/cmaa2a4dieqn003.gif] {{{T}_{̑ext{c}}}≈ 4.2} K) and IMG [http://ej.iop.org/images/0953-8984/28/34/345701/cmaa2a4dieqn004.gif] {̑ext{La}{{łeft(̑ext{C}{{̑ext{o}}_{0.7}}̑ext{F}{{̑ext{e}}_{0.3}}˚ight)}_{2}}{{̑ext{B}}_{2}}} ( IMG [http://ej.iop.org/images/0953-8984/28/34/345701/cmaa2a4dieqn005.gif] {{{T}_{̑ext{c}}}≈ 5.8} K). The site selective NMR experiment reveals the multiband nature of the Fermi surface in these systems. The temperature independent Knight shift and 1/ T 1 T clearly indicate the absence of correlated low energy magnetic spin-fluctuations in the normal state, which is in contrast to other Fe-based pnictides. The density of states (DOS) of Co 3 d electrons has been enhanced in superconducting IMG [http://ej.iop.org/images/0953-8984/28/34/345701/cmaa2a4dieqn006.gif] {̑ext{L}{{̑ext{a}}_{0.9}}{{̑ext{Y}}_{0.1}}̑ext{C}{{̑ext{o}}_{2}}{{̑ext{B}}_{2}}} and IMG [http://ej.iop.org/images/0953-8984/28/34/345701/cmaa2a4dieqn007.gif] {̑ext{La}{{łeft(̑ext{C}{{̑ext{o}}_{0.7}}̑ext{F}{{̑ext{e}}_{0.3}}˚ight)}_{2}}{{̑ext{B}}_{2}}} with respect to the non superconducting reference compound IMG [http://ej.iop.org/images/0953-8984/28/34/345701/cmaa2a4dieqn008.gif] {̑ext{LaC}{{̑ext{o}}_{2}}{{̑ext{B}}_{2}} . The occurrence of superconductivity is related to the DOS enhancement
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Torsional responses of double-walled carbon nanotubes via molecular dynamics simulations
No full text10.1088/0953-8984/20/45/455214Journal of Physics Condensed Matter2045-JCOM
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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